Destaticizing process



Patented July 24, 1951 UNITD STATES rice:

DESTATICIZIN G PROCESS corporation of Delaware No Drawing. Application April 4, 1950,v Serial No. 154,002

7 Claims. (Cl. 250-106) This invention relates to processes for rendering non-conductive materials resistant to the development of electrical charges by static excitation and to the materials so treated. More particularly, the invention relates to destaticized non-conductive materials and to a process for destaticizing non-conductive materials by radioactive means;

Non conductive materials such as glass, porcelain,'cellulose films and webs, cellulose derivative articles, synthetic resin articles, etc. easily acquirefa static charge. The charge may become strong enough to give a disconcerting jolt toan individual who discharges it by bodily contact. Moreover, the static charge causes dust and lint to accumulate on the surface of thenonconductive material.

' Many means for rendering non-conductive materials resistant to static excitation have been proposed most of which depend either .on operating under condtions of controlled humidity, or on the incorporation of hygroscopic material'into the electrically non-conductive materials. It has also been observed that exposure to radioactive materials will destaticize non-conductive materials for short periods of time.

' One object of this invention is to provide electrically non-conductive materials which are re-r sistant to the development of electrical charges by static excitation.

Another objectis to provide a process for rendering electrically non-conductive materials resistant to the development of electrical charges by static excitation. M

A particular object is to provide a process for destaticizing organic plastic materials.

"These and other objects are accomplished by subjecting electrically non-conductive materials to the'radiation of a mixture of a radioactive materialwith boron or beryllium.

A simple and efiective test for static electricity charges on the non-conductive materials is as follows:

Place dry cigarette ashes on a smooth insulated wooden surface in an atmosphere having a controlled relative humidity of about 20%, rub the non-conductive material vigorously with a piece of soft cloth and then bring the rubbed surface to about from the cigarette ashes. a slight charge will cause the ashes to fly to the non-conductive material and adhere thereto.

The following examples are given in illustration and are not intended as limitations of the Even scope of this invention. Where parts are mentioned they are parts by weight.

Example I sule and the capsule is imbedded in a block of: The dimensions of the paraflin are' parafiin. such that a layer of about 4 inches of paraffin surround the entire capsule; This paraflin en-1 closed capsule is then used for destaticizing nonconductive materials by placing it in close juxtaposition thereto. Flat discs of polystyrene containing about 0.1% of zinc stearate, polyvinyl chloride containing about 0.2% of triphenyl stibine become destaticized after about 1 hour in contact with the parafiln' block containing the radioactive capsule. by-the cigarette ash test, no amount of rubbing caused the development of electrostatic charges thereon. The antistatic properties remain undiminished for more than a year.

In contrast to the, treated discs of the example, untreated discs of the same materials picked up a strong electrostatic charge With but slight rubbing. A polystyrene disc, for example,

picks up a strong enough charge to attract dry cigarette ashes from a distance of more than /2".

Example II Example-I is repeated except that powdered boron is used instead of beryllium, The results are substantially the same and the resistance to the development of an electrostatic charge remains effective over long periods of time.

If a disc of polystyrene is subjected to'the direct action of the radiation from radium bro-' mide, it quickly becomes destaticized but the eiTect of the radiation fades rapidly and disappears almost entirely within -2 or 3 hours.

Example III Ten pieces of platinum foil coated with polonium are superimposed andplaced between plates of boron carbide. .The laminar structure thus made is inserted into a thin-walled brass box and the box placed in a graphite container having walls about 3 inches thick. The ratio of polonium to combined boron is about :400 on a weight basis. A sheet of polyvinyl chloride containing a small amount of a phosphotungstate dye becomes completely destaticized When tested 3 after exposure to the radiation from the graphite container. The effective resistance to the development of electrostatic charges remains unchanged for more than a year.

Example I V An aqueous solution containing thorium tetrachloride and boron bromide in proportions equivalent to 100 parts of combined thorium and 300 parts of combined boron is, dried by gentle heating. The dried material is then pelletized and enclosed in a brass capsule which is in turn enclosed in a substantially pure polystyrene container having walls four inches thick. Non-conductive materials including paper, polystyrene and polymerized methyl methacrylate, each of which contain small amounts -of a zinc salt, are rendered impervious to the development of electrostatic charges by short exposure to the polystyrene enclosed radioactive material.

The destaticizing'agents of'this invention are combinations of radioactive materials with boron or beryllium or a mixture of boron and beryllium. Among the radioactive materials which may be used are ionium, radium, radon, polonium, protactinium, thorium, actinium, and mixturesthereof. The radioactive materials may be used in their elemental form or in the form.

of their organic or inorganic derivatives. The destaticizing agent may be in the form of. an intimate mixture of the radioactive material with the boron or beryllium or the latter may be interposed between the radioactive material and the non-conductive object so that the radiations must pass through the boron or berylliumbefore reaching the non-conductive material- As shown in the examples, the intimate mixture may be obtained by dissolving water-soluble salts of each of the components in water and then evapcrating the water or by dissolving a watersoluble salt of the radioactive element in water and, forming a slurry with pulverulent boron, beryllium or insoluble derivatives thereof. The ratio of radioactive material to boron orberyllium should be regulated on the basis of the radioactive element and elemental boron or.

beryllium. For every 100 parts of radioactive element, either alone or chemically combined,

there should be from 100 to 1000.parts of ele-- mental boron or berylliumeither alone or chemiically combined.

Other elements than boron'and beryllium are either inoperative or so diificult to employ that they are useless in-the process of this invention. Boron or beryllium may be used per se or they may be used. in the form of their organic or inorganic derivatives. The insoluble derivatives may be used in pulverulent form or in the formof thinfilms or sheets.

The combination of the radioactive material with-the boron or beryllium is convenientlyenclosed. ina thin-walled-metal container such as" materials such as graphite, parafl'in, polymers of ethylene, isobutylene, styrene, etc. may be used providing these material are substantially pure and free from metallic elements.

In order for the radiation from the. radioactive compositions to accomplish the destaticizing action, there must be present in parts of the non-conductive materials at least 0.05 part of certain metals either in the elemental form or chemically combined. Among the most effective metals are antimony, zinc and silver. Less effective metals are tin, calcium, scandium, titanium, selenium, strontium, zirconium, indium, cerium, tellurium, gadolinium, terbium, thulium, tantalum, tungsten, osmium, iridium, mercury and lead. Since many dyestufis, especially mordant dyes, lubricants, stabilizers and pigments contain sufiicient amounts of one or more of. the effective metals, it frequently isnot necessary to modify the non-conductive materialsltov insure incorporation of an activating metal. The incorporation of small amounts of. the. acti-, vating metals or their derivatives in 11011-76011.- ductive materials which do not contain them is generally accomplished with ease. I

The radioactive compositions of thisinvention retain their effectiveness for many years.. The amount of the compositions used determines; the exposure time necessary to render the non-con ductive material impervious to electrostaticexcitation. A large amount of the radioactive composition spread thinly over a large area may. be used to destaticize sheets and continuous; lengths of non-conductive materials. If the. radioactive composition is concentrated in a small area, the radiations therefrom will quickly penetrate relatively thick objects. These thick objects may then be molded, carved, machined, etc. and yet the new surfaces thus exposed will still be destaticized. V

The process of this invention is applicable: to. all electrically non-conductive materials which. contain the minimum amounts of the. activating. metals. Among. the materials which. may, be treated are glass, wood, paper, natural and syn-* thetic organic materials such as regenerated cellulose, cellulose ethers and esters, naturalor synthetic. rubber, organic plastics such as phenolic resins, urea resins, melamine.resins-,..poly-' styrene, polyethylene, vinyl chloride. polymers and copolymers, polymers and copolymers of other vinylidenecompounds, etc. The non-cone, ductive materials may be in the shapeoffsheeta, rods, tubes, fibers, molded andextruded-designs, etc.

The process of this invention is advantageous in that it provides a quick method forrendering, electrically non-conductive materials resistant to electrostatic excitation over a relativelylong period of time.

What is claimed is:

1. A process which comprises placing radio-' active material in substantial contact with a substance from the group consistingof elemental and chemically combined boron and beryllium, thereafter embedding the" radioactive material and said substance-in a casing havingwalls from 2 to 6 inches thick, saidcasing comprising a solid 'material taken from. the groupconsisting of carbon and hydrocarbons, and subjecting" anon-conductive material to the radiations ema:- nating from the'casing, said non-conductivematerial containing-at least 0.05% by weight-of:a* substance from the group consisting of elemental and chemically combined zinc, silver, antimony, calcium, scandium, titanium, selenium, strontium, zirconium, indium, tin, tellurium, cerium, gadolinium, terbium, thulium, tantalum, tungsten, osmium, iridium, mercury and lead.

2. A process as in claim 1 wherein the radioactive material is radium bromide.

3. A process as in claim 1 wherein the radioactive material is polonium.

4. A process as in claim 1 wherein the substance associated with the radioactive material is beryllium.

5. A process as in claim 1 wherein the substance associated with the radioactive material is boron.

6. A process as in claim 1 wherein the nonconductive material is an organic polymer.

7. A substantially permanently destaticized non-conductive material comprising a nonconductive material containing at least 0.05% by weight of a substance taken from the group consisting of elemental and chemically combined zinc, silver, antimony, calcium, scandium, titanium, selenium, strontium, zirconium, indium,

6 1 tin, tellurium, cerium, gadolinium, terbium, thulium, tantalum, tungsten, osmium, iridium,

CHARLES KILBO-URNE BUMP. HAROLD F. PARK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,048,490 Bilstein July 21, 1936 2,264,683 Smith Dec. 2, 1941 2,479,882 Wallhausen et a1. Aug. 23, 1949 

1. A PROCESS WHICH COMPRISES PLACING RADIOACTIVE MATERIAL IN SUBSTANTIAL CONTACT WITH A SUBSTANCE FROM THE GROUP CONSISTING OF ELEMENTAL AND CHEMICALLY COMBINED BORON AND BERYLLIUM, THEREAFTER EMBEDDING THE RADIOACTIVE MATERIAL AND SAID SUBSTANCE IN A CASING HAVING WALLS FROM 2 TO 6 INCHES THICK, SAID CASING COMPRISING A SOLID MATERIAL TAKEN FROM THE GROUP CONSISTING OF CARBON AND HYDROCARBONS, AND SUBJECTING A NON-CONDUCTIVE MATERIAL TO THE RADIATIONS EMANATING FROM THE CASING, SAID NON-CONDUCTIVE MATERIAL CONTAINING AT LEAST 0.05% BY WEIGHT OF A SUBSTANCE FROM THE GROUP CONSISTING OF ELEMENTAL AND CHEMICALLY COMBINED ZINC, SILVER, ANTIMONY, CALCIUM, SCANDIUM TITANIUM, SELENIUM, STRONTIUM ZIRCONIUM, INDIUM, TIN, TELLURIUM, CERIUM, GADOLINIUM, TERBIUM, THULIUM, TANTALUM, TUNGSTEN, OSMIUM, IRIDIUM, MERCURY AND LEAD. 